Bug 7308: (follow-up) removing line breaks for better translatability

Bug 7308: (follow-up) removing line breaks for better translatability

Because of the lines breaks in the table headings the strings
were separated in translation. Example:

Base-level allocated
 - Base-level
 - allocated

If you look at a smaller screen the table headings will still break
without the additional <br />.

Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: Galen Charlton <gmc@esilibrary.com>
(cherry picked from commit 3c54feb1b3e15ddeca23adad1bec45e29dfeb1d5)
Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>